Imaging systems, such as computer to plate (CTP) systems, are well known in the art. Imaging systems record an image on a film or plate. Plates are typically made of an aluminum substrate with a photosensitive emulsion applied to one surface. Plates of a variety of substrate and emulsion compositions are possible, including emulsions with a variety of imaging characteristics (e.g. exposure energy density, image working sense, and run length). Additionally, plate formats range to accommodate a variety of page (e.g. letter size) layouts. For example, plates sized to accommodate a single page up to a plate sized to accommodate thirty-two, sixty-four or more pages are known in the art. Thus, an imaging system can be called upon to process a wide variety plate types.
Manufacturers typically deliver plates in a stack of equivalently sized plates, separated by protective interleaf slipsheets. A plate stack can be delivered on a pallet or other structure that provides support and simplifies conveyance. Alternatively, a plate stack can be delivered in a carton or other protective enclosure. Larger sized plates are difficult to transport and store because of their size, weight and susceptibility to damage.
For many reasons, such as maximizing throughput, and maximizing unattended operating time, many imaging systems provide integrated storage facilities for a quantity of plates that are likely to be used and automated mechanisms for selecting and transporting a plate to be imaged. Prior art imaging systems have incorporated integrated storage of plate stacks. However, it is a challenge to provide for a sufficient quantity of an appropriate variety of plate sizes while minimizing floor space usage.
Loading of a quantity of plates into an imaging system's integrated storage facility, especially large format plates, can be difficult because of their size and weight. Individual plates can weigh between at least 700 g for an 8-up format and at least 2 kilograms for large formats. Storage of 50 plates or more of a given size is desirable to allow the imaging system to operate without user attendance.
Imaging system cassettes, trays, bays or other mechanisms have traditionally been used to constrain the orientation of loaded plates so that plate picking and transport can be reliably accomplished. Storage areas typically contain one or more plate edge stops, guides or other mechanical devices to constrain the loaded plate orientation. For example, a plate bay, housing a carton of plates stacked horizontally and resting on one edge, comprises a stop (bay floor) for supporting one end of the carton which constrains the horizontal plate stack in one dimension. As another example, a plate cassette will typically have at least two stops for adjacent plate edges to constrain the plate stack orientation in two dimensions. Manual loading of a significant quantity of plates into an imaging system storage facility that restricts placement may thus be a time consuming process.
Obtaining and disposing of protective interleaf slipsheets in response to a plate imaging operation presents additional challenges. Slipsheets tend to be attracted to either the plate picked for imaging or to the plate remaining on the top of a plate stack. Slipsheets are typically made of a flimsy and slippery material and so are easily damaged or can become misaligned with an adjacent plate. These characteristics make locating, obtaining and transporting a slipsheet challenging. Additionally, if a slipsheet becomes creased or folded, it can damage the emulsion on the plate it is protecting if it is subsequently dragged across the emulsion surface.
Disposal presents an additional challenge with prior art systems ejecting them from the imaging system or crumpling them and storing them in an internal storage bin. The former method results in additional floor space requirements and can present aesthetic or safety problems. The latter method provides for an efficient use of floor space but suffers from problems of limited capacity, complicated and error-prone mechanics (e.g. slipsheet jams). An additional object of the present invention is to dispose of slipsheets internal to the plate handling system by stacking them vertically. This minimizes storage space, simplifies unloading and transport for final disposal, and presents an opportunity for reuse of the slipsheets.